Method of making self-locking screws



Patented Feb. 21, 1939 4 UNITED STATES Manton oF MAKING snm-momo scaawsYy Joseph H. Hoorn, Saginaw, Mich., assigner, by mesne assignments, toEaton Manufacturing gslilllnpany, Cleveland, hio, a corporation ofApplication December 23,` 1935, Serial No. 55,712 1 claim. (ci. zia-14s)This invention relates to a novel and improved method of manufacturingself-locking screws.

' More particularly the present invention relates to an improved methodof manufacturing composite threaded machine screws, which when screwedinto a suitable threaded recess serve to lock kthemselves automaticallyin predetermined position and which are not readily subject todisplacement or rotation as the result of vibration or other stressesimposed upon them.

Screws .of the generaltype with which the method of the presentapplication is primarily concerned generally comprise a head portionadapted tobe engaged by wrench or any other suitable means and athreaded shank. The shank portion of the screw is provided with an axialextension of substantially reduced diameter and of non-cylindricalcross-section. As will hereinafter be more clearly seen, Ithe particularcross-section of this extension portion is more' or less immaterialexcept that it serves to prevent relative rotational movement of a lockelement which is mounted for axial movement thereon. The lock elementhas its peripheral surface threaded with threads of the same diameterand pitch as those on the screw shank and is slidably mounted upon thisextension portion.v A helical coil spring, which has one end anchoredadjacent the terminal end of the extension portion, bears against theouter axial face of the lock element, thus normally urging it closelyinto engagement with the axial face of the shank portion of the screw.As will hereinafter be clearly seen, the.. threads on the shank of Ithescrew and those on4 the peripheral surface of the lo'ck element aremismatched. That is, when the members are urged closely into engagement,the thread of one does not constitute a continuation of the thread of.the other. It is essential to screwsof this general character that thisoiset relation exist in order that the element will exercise effectivelocking action. I y

It is a general object of the present invention to provide a relativelysimple and extremely practical method of manufacture for self-flockingscrews of this general type.

Still further it is an object of the present invention to provide aself-locking screw construction of the type defined above in which theangular degree or extent to which the-threads on the shank of the screwand threads on the peripheral surface of the lock element aremismatched. is accurately determined.

Yet another object of the present invention is to provide a method formanufacturing selflocking screws of this general class in which thepoint at which the thread lead on the screw shank ends is accuratelypositioned with respect to the non-cylindrical extension formed on theshank of the screw.

Still further the present invention contemplates the provision of amethod for manufacturing lock elements provided with apertures having aconilsuration adapted to receive the particular extension formed on theshank of the screw and'of a method for threading the peripheral surfacesof these lock elements in order that the lead of the thread at thepoint-where it commences will have a definite, predetermined angularposition with respect to the configuration of the aperture through theaxial portion of the lock element, in order that when the lock elementis fitted on to the improved screw, a definite predetermined angularityor offset between the adjacent lterminal ends of the respective threadedsurfaces will be obtained.

The present invention contemplates the provision of amethod in which ascrew shank and cooperating peripherally threaded lock element aremounted in coaxial non-rotatable 'position with respect to each other.The specific method of the presentinvention relates to a process forthreading the surface of the screw shank and the surface of the lockelement in such a manner that the points Where the lead of the threadabout the screw shank emerges from the axial end of the screw shank isangularly offset a substantial distance from the point where the lead ofthe thread on the lock element emerges from the adiacent axial endthereof.

In order to provide a method which will accomplish the above results, itwill be appreciated that. it is inherent that a method of threading theindividual parts must be provided in which the actuall point oi?emergence of the lead of the screw thread may be accurately controlledwith respect to the non-circular axial central portion of the memberbeing threaded. This exact control of these points is necessary in orderthat the lock element may be interchangeably used with various studs asmay be desired and as may be quite essential in order to simplifyassembly operations.

Still further the present invention contemplates the provision of amethod by which the threads may be formed simultaneously upon both the4shank of the screw and the peripheral surface of A spect to each other.In furtherance of this last mentioned object, the present inventioncontemplates the provision of a die which has two separate sets oiforming teeth thereon. one of said sets ci teeth being substantiallyoffset from the other in order that the adjacent ends of the threadleads on the two members will be oil'set from one another thepredetermined required angular distance.

In order that a more complete understanding of the present invention maybe had, reference is directed to the prior co-pending application ofzder. serial No. 40,009, med september 11, 1935, now Patent No.2,098,897, in which is shown specincally the tappet construction, which,as is explained hereinafter, may be conveniently manufactured by themethod of the present case.

Many other and further objects and advantages of the present inventionwill become apparent from the following specification when considered inconsideration with the accompanying drawing forming a part thereof.

In the drawing:

Fig. l is a vertical elevational view with parts in section illustratinga screw manufactured in accordance with the teachings of the presentinvention, showing the screw threaded into a suitable recess.

Fig. 2 is a top plan view of a blank from which the improved screw ismade, illustrating the beginning of the threading operation on the shankthereof.

Fig. 3 is a transverse sectional view taken on the line I-J of Fig. 2showing the manner in which the threading operation is commenced.

Fig. 4 is a top plan view of the completed screw member showing theshank thereof completely threaded.

Fig. 5 is a sectional view taken on the line 5 5 oi' Fig. 4 showing thecompletely threaded screw member.

Fig. 6 illustrates in perspective the blank i'rom which the lockingmember is formed.

Fig. 7 is a top plan view of the blank shown in threaded lock element.

Fig. 10 is an end view of the finished lock element.

Fig. ll is a top plan view of a screw manufactured in accordance with amodified form of the method of the present invention, in which thethreading oi' the shank portion of the screw takes piace prior to thedeformation or attening of the extension portion thereof.

Fig. l2 is a transverse sectional view taken on the lline |2-i2 of Fig.1i showing the completely threaded screw member prior to the flatteningof the extension portion thereof.

Fig. 13 is an end view of the screw element after the extension portionthereof has been preformed.

Fig. 14 shows a screw manufactured according to a modiiied form onf themethod of the present invention, in which both locking element and screwshank may be threaded in the same operation.

Pig. 15 is a sectional view taken on the line Il-Il of Fig. 14 showing across-sectional shape o! extension particularly adaptable for practicingthis modified form of the invention.

Fig. 16 is a plan view oi a composite rolling die adapted for thesimultaneous formation of threads on both the shank of the screw and thelock element member.

Fig. 17 illustrates the manner in which the threads are formedsimultaneously upon both the screw shank and the lock element member bymembers of the composite die oi the type shown lnFlg.16.

With more particular reference to the drawing, the improved self-lockingscrew member, to which the method oi the present invention is primarilydirected, is shown in completely assembled form in Fig. 1. While it willbe readily appreciated that the method of the present invention issusceptible of very many different uses in the manufacture ofself-locking screw elements of many and various types, by way ofilustration I have shown a particularly specific form oi screw elementwhich readily lends itself to manufacture by the method oi' the presentinvention. 'I'he screw element shown by way of illustration in Fig. 1,while susceptible of many and various uses, is primarily designed forthe adjustment of valve tappets in internal combustion engines. It haslong been appreciated that screws of this general type are particularlyadaptable for this specific use and in installations of this genericclass it is particularly desirable that the relative axial position oi'the screw member with respect to the member into which it is threadedmust be not only easily adjusted but must be accurately maintained afterthe adjustment has been made.

In the construction shown in Fig. 1 the screw comprises a cylindricalshank portion i threaded into a suitable casting 2. The shank portionmay be rotated by means of a suitable hexagonal head 3, preferablyformed integrally therewith and adapted to be engaged by a wrench orother sultable means, and having there above a head portion l adapted toreceive the base end of a valve push rod or valve stern 5. The shankportion i of the screw is provided with an axially extending projection8 oi reduced diameter which has one side thereof flattened in order thatthe projection 6 will be of non-circular -conguration Mounted on theprojection 6 and axially movable therealong is a lock element 1 having athreaded. outer periphery and having a central aperture of a congurationadapted to receive the projection 6 and preclude relative rotationalmovement between the lock element 1 and the main body portion of thescrew. A compression coil spring 8, having one end abutting the lockelement 'l and the other end abutting a suitable washer 9, disposedaround the projecting reduced portion of the screw l, positions the lockelement with respect to the shank of the screw. The washer 9 ispreferably retained in position by means of swaglng over the outer endof the extension of the screw shank. It will be appreciated from theconstruction described above that the lock element 1 is continuallyurged against the axial face of the threaded shank of the stud I. Aswill be more clearly seen hereinafter, the threads on the shank I and onthe peripheral surface of the lock element 'l are mismatchedsuiiiciently so that when both of these members threadably engage thethreaded recess in the casting 2 in which they are screwed, it isnecessary that some axial displacement of the lock element 'l take placewith respect to the threaded shank portion oi the screw in order thatthe threads on both these members will mate with the threads of thethreaded recess.

It will be seen that such axial displacement serves compression of thisspring, locking the stud as a whole in predetermined position withrespect to the recess in which it is screwed firmly enough to preventrelative rotation thereof under .the shocks and vibration to which it issubjected to in service, yet permitting it to be readily adjusted bymeans of a wrench.

One form of the improved method of manufacturing self-locking screws isshown in detail in Figs. 2 to 10 inclusive of the drawing. A blank isformed having a suitable head portion I5, a cylindrical shank I6 and anaxial extension I1 of reduced diameter. This axial extension ispreferably milled or ground to i'iatten one surface thereof at I8 tocreate a structure of unlform non-circular cross section throughout itsentire length. While the shank of the screw may be threaded in anysuitable manner by means of a rotary die or rolling dies, I have shownby way of illustration the threading operation being performed by meansof a conventional threading tool I9 oi' a lathe. Irrespective of theparticular means by which the shank I6 of the screw is threaded, it isessential that this threading operation is accurately controlled inorder that the lead of the thread cut on the shank will emerge from theaxial end of the shank at a predetermined point with' respect to theInattened surface Il of the axial extension i1. By reference to Fig.- 3,it may be seen that in the thread cut on the particular blank shown, bymeans of the tool I9, the point of emergence oi' the thread lead at theaxial end of the screw shank occurs at approximately the point 20.

It will be noted by reference to Figure that the point of emergence 20of the lead of the thread cut on the shank of the screw lies at a pointdiametrically opposite from the ilattened portion of the axialextension. As will hereinafter be seen, the angular position of thispoint of emergence is not important except in relation to the angularposition of the point of emergence of the thread lead on the adjacentportion of the locking element.

A cylindrical lock washer blank, shown in perspective in Figure 6, isprovided. 'I'his blank has a central aperture 26 of a conngurationadapted to t closely over tl'ie axial extension on the screw in orderthat the lock element will be freely axially movable with respect to thescrew, but non-rotatably mounted with respect thereto. The outsidediameter of this lock element is preferably identical with the outsidediameter of the screw shank and is threaded with a series of screwthreads of the same form and pitch. In order to perform this threadingoperation, the lock element is clamped on a suitable mandrel 21 as by anut such as 2l or by another suitable means, and while it may bethreaded by means of rolling dies or rotary dies, as may be desired,Figures 'I and 8 of the drawing disclose the threading operation beingperformed by means of a threading tool 29 of a lathe. It is likewiseextremely important in threading the peripheral surface of this lockelement that the lead of the thread will emerge from the axial end ofthe lock element at a predetermined point with respect to thenon-circular aperture-therein. 4As will be seen by reference to Figure8, the point of emergence of this thread lead lies at substantielly thepoint 30. It will be noted thatthis point of emergence 30 is adjacentthe attened portion of the aperture in the locking element andconsequently when the locking element is slid onto the projection on thescrew shank the point of emergence I0 will be angularly oisetapproximately 180 degrees from the point of emergence 20 of the lead ofthe thread on the screw shank. It will be appreciated that the degree ofthis angular offset relation of these thread leads may be varied withinrelatively wide limits. It will be appreciated that the degree ofangular offset between the points of emergence of these thread leadsdetermines the axial position to which the lock element must be movedaway from the adjacent end of the screw shank in order that the threadsof both members will lie in the same helix.

After the threading operation of the lock element has been completed,the lock element is slid on to the axial extension on thescrew and movedinto closely abutting relation with the axial end of the screw shank.Due to the noncircular connguration of the-axial extension l1 on thescrew shank and the complemental configuration of the aperture 26 in thecentral portion of the lock element, it will be appreciated thatrelative rotational movement between the lock element and the screw willbe' prevented. It will further be noted that the points of emergence ofthe thread lead on the screw shank and on the adjacent axial end of thelock element will be angularly offset from each other approximately 180degrees. The assembly operation is then completed by-mounting the springelement 8 around the end of the axial extension and securing this springelement in place by means of the washer 9 and upset end of the axialextension.

The lock element is then, at all times urged, into close engagement withthe adjacent axial face of the screw shank. It will therefore beapparent that the thread leads on the screw shank and on the peripheralsurfaces of the lock element lie in parallel helices, but due to theoilset relation of the point of emergence of the adjacent end of theseleads, the thread on one ele'- ment will not constitute a continuationof the thread on the other element and consequently the thread to thetwo members will be mismatched or otlset as long as the lock element isin closely abutting relation with the adjacent end of the screw shank.

Referring again to Figure l, it will be appreciated that asthe assembledself-locking screw is screwed into a threaded recess, the mismatching ofthe thread of the screw shank and lock element will cause a necessaryaxial movement of the lock element serving to compress the spring 8, theextent of this movement depending upon the angularity of offset betweenthe points of emergence of the thread leads on the two elements. Thislaxial movement is suillcient to establish a denite clearance betweenthe lock element and the end of the screw shank and consequently bymeans oi the spring 8 a constant tension is exerted upon theinter-engaging 'threaded portions. thus yieldably locking the screw inadjusted position.

A modified form of the invention is illustrated in Figures 11 to 13inclusive. In this form of the invention, a blank is provided having ahead portion 3l, a cylindrical threaded shank 38, and a cylindricalaxial extension 31 of reduced diameter, formed preferably integrallywith the shank of the screw. This modiiied method of manufacture ofscrews of this general type differs from the method described above inthat the shank of the screw is threaded prior to the flattening ordeformation of the. axial extennon thereon noem the-mt unsure malextension 31 is cylindrical at the time the threading operation isperformed, it may be appreciated that the shank of the screw may bethreaded in any suitable manner and after it has been threaded the axialextension I1 is milled or ground to provide a nat surface Il. 'Ihisnattened surface It is formed on a circumferential portion of the axialextension predetermined, with respect to the point of emergence Il ofthe lead of the thread on the screw shank. As was the case in thepreferred embodiment of the invention described above, this axialextension portion may be nattened upon the diametrically opposite sideof the screw from that on which 'the lead of the thread emerges. As hasbeen brought out above, this construction will create an angularity ofonset between the thread leads on the screw shank and locking element ofapproximately 180 degrees, but, as has been pointed out above thespecific extent of this angular onset is not important and may be variedwithin relatively wide limits. However, it is essential to the operationof the device that some onset rela-` tion exist. It will be appreciatedthat in this modified method of manufacture the resulting product issubstantially identical with that shown in Flg.`4 and described above,and that a lock element identical with the element shown in Fig. 9 maybe used with this member to provide an identical self-locking screwconstruction.

A still further modified method of manufacture of screws of this generaltype is shown in Figures 14 and l5. In this form of the invention ablank is provided having a suitable head portion 4I, a shank 4i and anaxial extension 42. 'nils axial extension l2 is of substantially reduceddiameter with respect to shank Il and is milled to provide iiat surfacesIl and u on diametrically opposite sides thereof. A lock element 45having an outside diameter substantially identical with that of thescrew shank 4i is preformed to provide an axial aperture therein of l aconfiguration adapted to receive the axial exy tension I2. 'This lockelement Il is slid onto the axial extension 42 and urged into closelyabutting relation with the axial end of the screw shank 4|. The lockelementandv screw shank Il are then bothfthreaded by means of a cuttingtool 41. It will be appreciated that while these members are in thisposition the lead of the thread on the lock element will lie in the samehelix as the lead of the thread on the screw shank. After the threadingoperation has been completed, the look element 45 may be slipped on theaxial extension 42 and rotated through 180 degrees and re-assembledtherewith. This step will serve to insure a proper onset or mismatchedrelation between the threads on the lock element and on the screw shank,and the resulting screw will then have substantially the same generalcharacteristics-as the screws formed by the method described above.

A still further modiiled form of the method disclosed herein isillustrated-in Figures viand 1'1. 'Ihis method utilizes a novel form ofrolling die which makes possible the simultaneous formation of threadsupon both the screw shank and on the peripheral surface of the lockelement while these two members occupy substantially their finalassembled position. In the method of this form of the invention, a pairof composite rolling dies of novel construction are aisne used for thesimultaneous formation of the threads on both the screw shank and lockelement. These improved composite rolling dies each preferably comprisesa pair of sections 50 and Ii which are preferably formed by locking theminside-by-side relation and cutting and/or grinding a plurality ofthread cutting grooves in the surfaces thereof. The die Il is of a widthsubstantially'the same as the axial length of the lock element Ito bethreaded and section i is of a width substantially the length of the,

threaded areal which it is desired to form on the screw shank. It willbe appreciated that after the grooves have been cut in the surfaces ofthese'v die members the threads of the section 50 will be matched withthose of the section Il and, consequently, it is necessary, in orderthat the method of the present invention may be satisfactorilypracticed, that a mis-matching or offset relation between thethread-forming grooves on the adjacent die sections be established.While this onset or mis-matching relation between the thread cuttinggrooves of the two sections il and Il may be established by grinding ormilling on the adjacent edges of the members until the required onset isobtained, Figure 17 of the drawing illustrates a shim or spacing elementl! mounted between the sections 50 and Il which has a thicknesssuillcient so that the threads rolled by the die member will lie inparallel but dinerent helices.

In practicing the improved method by use of rolling dies such as aredisclosed in Figure 17, a blank such as is illustrated in Figure 2 has alock element'blank, such as is shown in Figure 6, mounted thereon withthe axial face of the lock element 25 in closely abutting relation withthe axial end of the lshank portion I 6 of the screw. The screw shankand lock element are then rolled between a pair of dies each composed ofsections Il and 5l with a shim or spacing ele- Ament I2 between thesections thereof in order to establish the required onset or mismatchingof the threads to be formed. Consequently, it .will be appreciated thatthe threads formed on the shank of the stud and on the peripheralsurface of the lock element will be simultaneously rolled and will beprovided with adjacent lead ends having the desired angular onsetrelation with respect to each other.

'I'he specific methods set forthabove are merely illustrative of thegeneric inventive concept denned in the subjoined claim. Many other andfurther modifications and forms thereof will be apparent to thoseskilled in the art.

What is claimed is:

The -method of making self locking screws which comprises forming acylindrical extension on the shank of said screw, flattening the surfaceof said extension-on diametrically opposite sides, forming a lockelement having an aperture adapted to receive said extension and havinga peripheral surface substantially the same diameter as the shank ofsaid screw, assembling said screw and lock element in coaxial position,

cutting a continuous thread on the shank of

